text: A fourth group has also been discovered and members have three amino acids between the two cysteines and is termed CXC chemokine (or d-chemokines). The only CXC chemokine discovered to date is called fractalkine (or CXCL1). It is both secreted and tethered to the surface of the cell that expresses it, thereby serving as both a chemoattractant and as an adhesion molecule.